The objective of this research proposal is: 1) To evaluate those factors responsible for normal in vivo platelet survival and to determine possible differences in platelets obtained from different donors with special attention to the drugs that donor may have taken. 2) To investigate those factors that will permit platelets to maintain ATP levels and to function after storage. Time, plasma anticoagulant, oxygen availability and storage temperature will be evaluated for their effect on platelet ATP levels and metabolic activity in vitro, especially in relation to activity of the Kreb's citric acid cycle and to platelet levels of cyclic AMP. The relation between platelet function in vitro and survival of platelets post transfusion will be used to determine factors essential for more efficient platelet storage. In vitro studies will be performed to determine the relationship between serotonin uptake of stored platelets and in vivo effectiveness. A standardized anti-platelet agglutination test is being devised to provide a reliable measure for the detection of platelet isoantibodies. Thus a realistic evaluation of platelet transfusion therapy in severely thrombocytopenic leukemic patients and the determination of factors and mechanisms that influence these benefits will be possible.